Ultrasound imaging system and method for detecting position and orientation of a coherent reflector

ABSTRACT

A method and ultrasound imaging system for detecting a coherent reflector comprises acquiring ultrasound channel data from a volume with a probe including a 2D aperture, calculating a MRT from the ultrasound channel data, identifying a first angle of a projection of the coherent reflector in a plane parallel to the 2D aperture based on the MRT, detecting a line-shaped echo pattern in the ultrasound channel data, determining a second angle of the coherent reflector with respect to the 2D aperture, determining a position and an orientation of the coherent reflector based on the first angle and the second angle, enhancing a representation of the coherent reflector in an image generated based on the ultrasound channel data, and displaying the image on a display device after enhancing the representation of the coherent reflector.

FIELD OF THE INVENTION

This disclosure relates generally to an ultrasound imaging system andmethod for detecting a position and orientation of a coherent reflectorusing ultrasound channel data.

BACKGROUND OF THE INVENTION

It is desirable to use ultrasound imaging to detect and trackinterventional devices such as catheters, guide wires, biopsy needlesand other devices. Conventional techniques rely on data from othermodalities, such as x-ray imaging, to detect the position of theinterventional devices. Fluoroscopy, a form of x-ray imaging, providesaccurate positional information regarding the interventional device, butit exposes both the patient and the clinician to ionizing radiation.Long-term exposure to ionizing radiation is known to be stronglycorrelated with negative health effects. Additionally, x-ray imaging isnot well-suited for imaging soft tissue, and the knowledge about theprecise position of various soft tissue structures is importantinformation for the clinician to have during many interventionalprocedures. As such, clinicians either have to rely solely on thefluoroscopic images, which may lack vital information about soft tissuestructures, or they may need to rely on multiple different imagingmodalities. Using multiple imaging modalities either requires specificsoftware to fuse the images together, or the clinician must mentallyperform the fusion. In any type of image fusion, there is always therisk that the images may be misregistered, leading to a less precise, oreven an ultimately unsuccessful, interventional procedure.

Ultrasound imaging is a non-ionizing modality that excels at imagingsoft tissue. Conventional ultrasound techniques are not well-suited forimaging interventional devices, which are typically coherent reflectors.Ultrasound beamforming techniques typically assume that receivedacoustic reflections come from diffuse scatterers that reflectultrasound energy in substantially all directions. This assumptionproves useful and effective when imaging soft tissue in a patient.However, the underlying physics for coherent reflectors is significantlydifferent than for diffuse scatterers. A coherent reflection is amirror-like reflection obtained from insonifying a hard level surfacewith ultrasonic energy. Coherent reflections are common when imaginghard or metal objects, such as catheters and biopsy needles. Ultrasoundechoes reflected from a coherent reflector behave according to Snell'slaw, which means that the angle of incidence is equal to the angle toreflection. Instead of reflecting ultrasound energy in substantially alldirections, as is the case with a diffuse reflection, coherentreflections are typically very strong at positions where an angle ofreflection of the reflected beam is equal to an angle of incidence.Specular reflections typically generate very little signal at most otherlocations. As such, ultrasound imaging systems only receive a signalfrom a coherent reflector if the transducer array is positioned toreceive the reflected echo. Many of the echoes reflected from a coherentreflector do not intersect with the transducer array and are thereforenot useful for constructing an image of the coherent reflector.

It is desirable to use ultrasound imaging to detect and track thereal-time position of coherent reflectors such as catheters, guidewires, needles and other interventional devices. Standard beamformingtechniques assume that the reflectors behave as diffuse scatterers. Assuch, standard beamforming techniques typically sum signals from aplurality of channels in order to form an ultrasound image. While thisapproach has proven very effective for soft tissue and othercircumstances where the imaged material behaves as a diffuse scatterer,it is ineffective when imaging coherent reflectors. The coherentreflector will not contribute significant signal to elements when thereflected beam is away from the probe. And, if a conventionalbeamforming technique is applied to ultrasound data including a coherentreflection, the contributions of the coherent reflector tend to getminimized during the summing process. Therefore, conventionalbeamforming techniques are not effective for imaging coherentreflectors.

Conventional systems may use an external tracking system, such as anelectromagnetic tracking system or an optical tracking system, todetermine the position and orientation of an interventional device inreal-time. However, using an external tracking system adds additionalexpense and complexity to the entire system. Additionally, theultrasound system is required to be configured to interface with thetracking system if data showing the location and/or the trajectory ofthe interventional device is to be displayed in real-time.

It is also known to use a needle guide that acts as a fixture keepingthe probe in a constant relative position with respect to a needle beingimaged. While this technique is effective for imaging needles, theneedle guide combined with the probe and the needle is bulkier andpotentially more difficult to maneuver than a stand-alone needle.Additionally, this technique does not work to track other types ofinterventional devices that are disposed completely within the patient.In ultrasound biopsy, the needle guide is typically used to guide theneedle into the tissue so that the needle is orthogonal to the transmitbeam. In a 2D B-mode scan it is difficult for the operator to determineif the tip of the needle is inside the image frame. Determining if thetip of the needle is inside the 2D image typically involves a fair dealof trial- and error by inserting and retracting the needle. Conventionaltechniques are currently not well-suited for determining if the needletip is inside of the 2D image frame. Conventional techniques relycompletely upon operator experience to ensure that the needle tip isvisible within the 2D image frame. As such, it is desirable to have anautomated method to adjust the position of the 2D image frame so thatthe tip is visible in the 2D image frame.

While performing an interventional procedure, it is often very importantto know the position and orientation of the interventional device, suchas a needle, a catheter, or any other type of interventional device bothto achieve the desired clinical outcome and to avoid potentiallydamaging surrounding tissue. For these and other reasons an improvedmethod and ultrasound imaging system detecting and tracking coherentreflectors, such as catheter, guidewires, and biopsy needles is desired.

BRIEF DESCRIPTION OF THE INVENTION

The above-mentioned shortcomings, disadvantages and problems areaddressed herein which will be understood by reading and understandingthe following specification.

In an embodiment, a method of detecting a coherent reflector with anultrasound imaging system including a processor and a display deviceincludes acquiring ultrasound channel data from a volume with a probeincluding a 2D aperture, calculating with the processor a Modified RadonTransform (MRT) from the ultrasound channel data. The method includesidentifying with the processor a first angle within a plane parallel tothe 2D aperture where the MRT is at least one of a maximum value orabove a threshold value. The method includes detecting, with theprocessor, a position of a line-shaped echo pattern in the ultrasoundchannel data, where the line-shaped echo pattern is produced by areflection from the coherent reflector. The method includes determining,with the processor, a second angle of the coherent reflector withrespect to the transmit aperture based on the position of theline-shaped echo pattern, determining, with the processor, a positionand an orientation of the coherent reflector based on the first angleand the second angle. The method includes enhancing a representation ofthe coherent reflector in an image generated from the ultrasound channeldata based on the MRT and displaying the image including the enhancedrepresentation of the coherent reflector.

In an embodiment, an ultrasound imaging system includes a probe with a2D aperture, a display device, a receiver in electronic communicationwith the probe, and a processor in electronic communication with thereceiver and the display device. The processor is configured to acquireultrasound channel data from a volume with the probe, calculate a MRTfrom the ultrasound channel data, identify a first angle within a planeparallel to the 2D aperture where the MRT is at least one of a maximumvalue or above a threshold value, and detect a position of a line-shapedecho pattern in the ultrasound channel data, where the line-shaped echopattern is produced by a reflection from the coherent reflector. Theprocessor is configured to determine a second angle of the coherentreflector with respect to the transmit aperture based on the position ofthe line-shaped echo pattern, determine a position and an orientation ofthe coherent reflector based on the first angle and the second angle,enhance a representation of the coherent reflector in an image generatedfrom the ultrasound channel data based on the MRT, and display on thedisplay device, the image including the enhanced representation of thecoherent reflector.

Various other features, objects, and advantages of the invention will bemade apparent to those skilled in the art from the accompanying drawingsand detailed description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an ultrasound imaging system inaccordance with an embodiment;

FIG. 2 is a flow chart of a method in accordance with an embodiment;

FIG. 3 is a schematic representation showing a coherent reflector withrespect to a 2D aperture;

FIG. 4 is a schematic representation showing a coherent reflector withrespect to a 2D aperture in accordance with an exemplary embodiment;

FIG. 5 is a schematic representation showing a 2D aperture with respectto a coherent reflector in accordance with an exemplary embodiment;

FIG. 6 is a schematic representation showing a reflection pattern inaccordance with an exemplary embodiment;

FIG. 7 is a “bird's eye” view showing a 2D aperture positioned withrespect to a coherent reflector;

FIG. 8 is a schematic representation of how a Modified Radon Transformmay be applied to ultrasound data according to an exemplary embodiment;

FIG. 9 is a representation showing an echo pattern and a correspondingMRT for three different orientations of a coherent reflector accordingto an exemplary embodiment;

FIG. 10 is a schematic representation of a conventional delay-and-sumbeamforming technique in accordance with an embodiment;

FIG. 11 is schematic representation of a delay-and-MRT beamformingtechnique in accordance with an exemplary embodiment

FIG. 12 is a schematic representation of a filter-delay-and-MRTbeamforming technique in accordance with an exemplary embodiment;

FIG. 13 is a representation of a comparison between images generatedusing delay-and-sum beamforming and images generated using delay-and-MRTbeamforming in accordance with an exemplary embodiment;

FIG. 14 is a schematic representation showing how a frame may be steeredaccording to an exemplary embodiment; and

FIG. 15 is a schematic representation of an image including a graphicalindicator in accordance with an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific embodiments that may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the embodiments, and it is to be understood thatother embodiments may be utilized and that logical, mechanical,electrical and other changes may be made without departing from thescope of the embodiments. The following detailed description is,therefore, not to be taken as limiting the scope of the invention.

FIG. 1 is a schematic diagram of an ultrasound imaging system 100 inaccordance with an embodiment. The ultrasound imaging system 100includes a transmit beamformer 101 and a transmitter 102 that driveelements 104 within a probe 106 to emit pulsed ultrasonic signals into atissue (not shown). The probe 106 may be a 1.25D array probe, a 1.5Darray probe, a 1.75D array probe, or a 2D matrix array probe. The 2Dmatrix array probe may allow for full steering in both the azimuth andelevation directions. The pulsed ultrasonic signals are back-scatteredfrom structures in the tissue, like blood cells or muscular tissue, toproduce echoes that return to the elements 104. The echoes are convertedinto electrical signals, or ultrasound channel data, by the elements104, and the electrical signals are received by a receiver 108. Forpurposes of this disclosure, the term “ultrasound channel data” will bedefined to include ultrasound data from a plurality of differentchannels/elements prior to beamforming. Ultrasound channel data maytherefore refer to data from either the probe 106 or the receiver 108.The processor 110 receives the ultrasound channel data from the receiver108. The processor 110 may comprise one or more processors including anyone or more of the following: a graphics processing unit (GPU), amicroprocessor, a central processing unit (CPU), a digital signalprocessor (DSP), or any other type of processor capable of performinglogical operations. The processor 110 may comprise a softwarebeamformer, but it should be appreciated that the processor 110 may beseparate from the software beamformer in other embodiments. As statedabove, the processor 110 receives ultrasound channel data from thereceiver 108. The processor 110 then applies the appropriate delays tothe ultrasound channel data in order to focus on specific locationswithin a region or volume-of-interest.

The processor 110 may be adapted to perform one or more processingoperations according to a plurality of selectable ultrasound modalitieson the ultrasound channel data. The ultrasound channel data may beprocessed in real-time during a scanning session as the echo signals arereceived. For the purposes of this disclosure, the term “real-time” isdefined to include a procedure that is performed without any intentionaldelay. For example, an embodiment may acquire and display data at areal-time frame-rate of 7-20 frames/second. However, it should beunderstood that the real-time frame rate may be dependent on the lengthof time that it takes to acquire each frame of data. Accordingly, whenacquiring a relatively large region or volume of data, the real-timeframe-rate may be slower. Thus, some embodiments may have real-timeframe-rates that are considerably faster than 20 frames/second, whileother embodiments may have real-time frame-rates slower than 7frames/second. The data may be stored temporarily in a buffer (notshown) during a scanning session and processed in less than real-time ina live or off-line operation. Some embodiments of the invention mayinclude multiple processors (not shown) and/or multi-core processors tohandle the processing tasks assigned to processor 110 in the exemplaryembodiment shown in FIG. 1.

According to other embodiments (not shown), the processor 110 shown inFIG. 1 may be replaced with two or more separate components. Forexample, an embodiment may include a processor and a separate softwarebeamformer (not shown) that are both in parallel between the receiver108 and a controller 116. According to this embodiment, both theprocessor and the software beamformer would receive ultrasound channeldata from the receiver 108. The software beamformer would, for example,perform beamforming operations, and the processor would performcalculations related to the identification of coherent reflectors in theultrasound channel data. According to an embodiment, the processor maycalculate the position and orientation of the coherent reflectors in thedata and transmit coordinates specifying the positions and/ororientations of any coherent reflectors to the controller 116. Accordingto another embodiment, the software beamformer may generate an imagebased on the ultrasound channel data and the processor may produce asecondary image. The secondary image may, for instance, includeinformation showing a graphical indicator of a coherent reflector. Thecontroller 116 may display the secondary image as an overlay on top ofthe ultrasound image, or the secondary image may replace either some orall of the ultrasound image. Various ways of displaying informationrelated to any coherent reflectors will be described hereinafteraccording to various embodiments.

According to some exemplary embodiments, the probe 106 may contain thecomponents to do some or all of the transmit and/or the receivebeamforming. For example, all or part of the transmit beamformer 101,the transmitter 102, the receiver 108 and the processor 110 may besituated within the probe 106. The terms “scan” or “scanning” may alsobe used in this disclosure to refer to acquiring data through theprocess of transmitting and receiving ultrasonic signals. Additionally,the terms “data” or “ultrasound channel data” may be used in thisdisclosure to refer to either one or more datasets acquired with anultrasound imaging system. A user interface 115 may be used to controloperation of the ultrasound imaging system 100, including, to controlthe input of patient data, to change a scanning or display parameter,and the like.

The ultrasound imaging system 100 also includes the controller 116 tocontrol the transmit beamformer 101, the transmitter 102, and thereceiver 108. The controller 116 may control the processor 110 accordingto some embodiments. According to other embodiments, the processor 110may be a sub-component of the controller 116. According to otherembodiments, the processor 110 may output images for display directly tothe memory 120 or to the display device 118, instead of transmittingprocessed data to the controller 116 as shown in FIG. 1. Referring backto FIG. 1, the controller 116 is in electronic communication with theprobe 106. The controller 116 may control the probe 106 to acquire data.The controller 116 controls which of the elements 104 are active and theshape of a beam emitted from the probe 106. According to someembodiments, the elements in the probe may be configured into aplurality of sub-apertures and the controller 116 may implementsub-aperture beamforming based on output from the sub-apertures. Thecontroller 116 is also in electronic communication with a display device118, and the controller 116 may process the ultrasound channel data intoimages for display on the display device 118. For purposes of thisdisclosure, the term “electronic communication” may be defined toinclude both wired and wireless connections. The controller 116 mayinclude a central processor according to an embodiment. According toother embodiments, the controller 116 may include other electroniccomponents capable of carrying out processing functions, such as adigital signal processor, a field-programmable gate array (FPGA) or agraphic board. According to other embodiments, the controller 116 mayinclude multiple electronic components capable of carrying outprocessing functions.

The ultrasound imaging system 100 may continuously acquire ultrasoundchannel data at a frame-rate of, for example, 10 Hz to 30 Hz. Imagesgenerated from the ultrasound channel data may be refreshed at a similarframe-rate. Other embodiments may acquire and display ultrasound channeldata at different rates. For example, some embodiments may acquireultrasound channel data at a frame-rate of less than 10 Hz or greaterthan 30 Hz depending on the size of the region-of-interest and theintended application. A memory 120 is included for storing processedimage frames for display at a subsequent time. Each image frame mayinclude an associated time stamp indicating the time or relative time ofacquisition to facilitate retrieval in the proper sequence from thememory 120. The memory 120 may comprise any known data storage medium.

In various embodiments of the present invention, ultrasound channel datamay be processed by other or different mode-related modules by theprocessor 110 (e.g., B-mode, Color Doppler, M-mode, Color M-mode,spectral Doppler, Elastography, TVI, strain, strain rate, and the like)to form 2D or 3D data. For example, one or more modules may generateB-mode, color Doppler, M-mode, color M-mode, spectral Doppler,Elastography, TVI, strain, strain rate and combinations thereof, and thelike. The image beams and/or frames are stored and timing informationindicating a time at which the data was acquired in memory may berecorded. The modules may include, for example, a scan conversion moduleto perform scan conversion operations to convert the image frames fromcoordinates beam space to display space coordinates. A video processormodule may be provided that reads the image frames from a memory anddisplays the image frames in real time while a procedure is beingcarried out on a patient. A video processor module may store the imageframes in an image memory, from which the images are read and displayed.

FIG. 2 is a flow chart of a method in accordance with an exemplaryembodiment. The individual blocks of the flow chart represent steps thatmay be performed in accordance with the method 200. Additionalembodiments may perform the steps shown in a different sequence, and/oradditional embodiments may include additional steps not shown in FIG. 2.The technical effect of the method 200 is the display of an image withan enhanced representation of a coherent reflector.

Referring now to FIGS. 1 and 2, at step 202, the controller 116 controlsthe transmit beamformer 101, the transmitter 102, and the probe 106 toacquire ultrasound channel data. The probe includes a 2D aperture usedfor transmitting and receiving ultrasound energy. The ultrasound channeldata may comprise 2D ultrasound channel data or 3D ultrasound channeldata. Each channel may carry the data from one or more elements 104 inthe probe 106. The ultrasound channel data may be acquired along aplurality of lines in a direction substantially perpendicular to theface of the probe 106 or some or all of the lines may be steered ineither an azimuth or an elevation direction and are not necessarilyperpendicular to the face of the probe 106. According to anotherembodiment, unfocused ultrasound energy may be used to acquireultrasound channel data during step 202. For example, plane waves,spherical waves, or any other type of unfocused transmission schemes maybe used to acquire the ultrasound channel data during step 202 inadditional to various types of focused transmit beams. The controller116 may, for instance, control the transmit beamformer 101 and thetransmitter 102 to emit a transmit beam with a discrete focal pointwithin the region or volume-of-interest. Next, the probe 106 receivesreflected ultrasound signals from along each scan line. The receiver 108receives unprocessed or raw ultrasound channel data from all of theelements 104 that are in the active receive aperture of the transducerarray. The processor 110 may process the ultrasound channel data inorder to generate pixel or voxel values at a plurality of differentpoints representing different depths along each scan line. The processor110 has access to the raw ultrasound channel data representing data fromeach channel. After receiving the raw ultrasound channel data, theprocessor 110, which may be a software beamformer according to anembodiment, may apply the appropriate delays to the ultrasound channeldata in order to focus at specific depths along each scan line. Theprocessor 110 may also emulate a conventional hardware beamformer anddynamically focus the receive beam as a function of depth along eachscan line. The software beamformer may be configured to performmulti-line acquisition (MLA). For example, the processor 110 may acquire2, 4, 6, 8, or 16 receive lines for each transmit line. It should beappreciated that the processor 110 may acquire a different number ofreceive lines for each transmit line according to other embodiments.

According to another acquisition scheme, the controller 116 may controlthe transmit beamformer 101 and the transmitter 102 to transmit two ormore waves with different foci, so that each location within afield-of-view is insonified from at least two different directions.Therefore, at least two samples are acquired from multiple directionsfor each location in the field-of-view. The processor 110 may receivethe ultrasound channel data from the probe 106 and apply retrospectivetransmit focusing (RTF) to the ultrasound channel data. When performingRTF, the processor 110 applies a time offset to at least one of the twoor more samples acquired at each location. The processor 110 may thencombine the samples after the offset has been applied. Applying theoffset allows for the samples to be combined in-phase and the processor110 can thus generate an image using the samples acquired based on twoor more different transmit events, each with a different focus.According to another embodiment, the controller 116 may control thetransmit beamformer 101 to emit unfocused ultrasound energy such as, forexample, plane waves or spherical waves.

At step 204, the controller 116 calculates a Modified Radon Transform(MRT, hereinafter) based on the ultrasound channel data. It is knownthat a coherent reflector produces coherent echoes. This means thatafter the time delays have been applied, echoes from a coherentreflector will be of the same or nearly the same phase.

Many of the figures described hereinafter show an elongated coherentreflector. As a convention, this structure will be referred to as a“coherent reflector” when describing the following figures in thisdisclosure. However, it should be appreciated that the coherentreflector may be a biopsy needle, a catheter, or any other type ofinterventional device or anatomical structure that would act as acoherent reflector according to various embodiments.

FIG. 3 is a schematic representation showing a coherent reflector 302with respect to a 2D aperture 304. FIG. 3 includes a transmit beam 308.The transmit aperture 304 includes a x-direction 310, a y-direction 312,and a z-direction 314. A longitudinal axis 306 of the coherent reflector302 is shown. FIG. 3 will be described in detail hereinafter.

Coherent reflectors with a generally circular cross-section, such asbiopsy needles, catheters, etc., produce various echo patterns, ordiffraction patterns, depending upon the orientation of the coherentreflector. For purposes of this disclosure, coherent reflectors will bedescribed as having a long, or longitudinal axis, and a sectional axis,which is defined to be perpendicular to the longitudinal axis. Forexample, FIG. 3 shows the longitudinal axis 306 and a sectional axis307.

FIG. 4 is a schematic representation showing a diffraction pattern for acoherent reflector in accordance with an exemplary embodiment. Thereflection is generated from a beam in a direction parallel to thelongitudinal axis 306 of the coherent reflector 302. FIG. 5 is aschematic representation showing a 2D aperture with respect to acoherent reflector 302 in accordance with an exemplary embodiment. Thereflection is based on a beam steered in a direction parallel to thelongitudinal axis 306 in FIG. 5 as well. FIG. 6 is a schematicrepresentation showing a diffraction pattern in accordance with anexemplary embodiment. In FIG. 6 the reflection is shown in the sectionaldirection that is perpendicular to the longitudinal axis. Thelongitudinal axis is in the direction into or out of the page and, assuch, is not represented in FIG. 6. FIG. 7 is a schematic representationshowing the 2D aperture 304 with respect to the coherent reflector 302in accordance with an exemplary embodiment. FIG. 7 is a “bird's eye”view showing the 2D aperture 304 positioned over the coherent reflector302. Common reference numbers will be used to describe identicalstructures in various figures.

FIG. 4 is a representation showing how an ultrasound beam 401 isreflected from the coherent reflector 302 in a direction parallel to thelongitudinal axis 306. The ultrasound beam 401 behaves according toSnell's law where an angle of incidence Θ_(i) is equal to an angle ofreflection Θ_(r), which are represented by β. In the example, both Θ_(i)and Θ_(r) are 90°. The ultrasound beam has an incident beam width 402that is the same as a reflected beam width 404.

FIG. 5 is a representation showing how an incident line 502 of anultrasound beam is reflected from the coherent reflector 302. Theincident line 502 may be part of an transmit ultrasound beam. Theorientation of the incident line 502 with respect to the coherentreflector 302 is different than that shown in FIG. 4. The surface normalof the coherent reflector 302 is disposed at an angle of β with respectto incident line 502. The reflected line 504 is reflected at an angle of2*β with respect to the incident line 502 The reflected line 504 isdetected by the 2D aperture 304 at a location 322.

FIG. 6 is a schematic representation showing how an incident ultrasoundbeam 601 is reflected by the coherent reflector 302 in a directionperpendicular to the longitudinal axis (not shown in FIG. 6). Afterreflecting from the coherent reflector 302 the ultrasound beam 601diverges. The incident ultrasound beam 601 has an incident beam width602, and the reflected ultrasound beam 604 has a reflected beam width606 that is significantly wider than the incident beam width 602 due tothe curved surface of the coherent reflector 302 in the directionperpendicular to the longitudinal axis. FIG. 6 includes a first normalline 608, a second normal line 610, and a third normal line 612. Each ofthe normal lines are shown normal, or perpendicular, to a surface of thecoherent reflector 302 at the position where the respective normal lineintersects the surface of the coherent reflector 302. The normal linesare disposed at different angles with respect to each other due to thecurved surface. This, in turn, causes incident ultrasound beam 402 todiverge after being reflected from the coherent reflector 302. While thecoherent reflector 302 shown in FIG. 6 has a circular cross-section, itshould be appreciated that coherent reflectors may not be perfectlycircular. As long as the surface of the coherent reflector is convexwith respect to the incident ultrasound beam in a directionperpendicular to the longitudinal axis, the coherent reflector willproduce a reflected beam that is wider than the incident beam in amanner consistent with that shown in FIG. 6. It should therefore beappreciated that other embodiments may be used to detect coherentreflectors with non-circular cross-sections. For example, otherembodiments may be used to detect coherent reflectors with an oval orelliptical cross-sections.

FIG. 7 is a schematic representation showing how an incident ultrasoundbeam is reflected from the coherent reflector 302 in a directionperpendicular to the longitudinal axis 306 of the coherent reflector302. The incident beam is not shown in FIG. 7, but it is directed at anorigin of an x-axis 702 and a y-axis 704 in a direction perpendicular tothe longitudinal axis 306. The 2D aperture 304 is represented in aposition above the coherent reflector 302. A line-shaped echo pattern322 represents the position where the reflected beam is detected by the2D aperture 304

FIG. 8 is a schematic representation of how a Modified Radon Transform(MRT, hereinafter) may be applied to ultrasound data according to anexemplary embodiment. FIG. 8 includes a 2D aperture 802 with x'srepresenting transducer elements. FIG. 8 includes the x-axis 310, they-axis 312, the projection of the longitudinal axis of the coherentreflector 320, and the line-shaped echo pattern 322. The MRT iscalculated for each individual angle Θ. The exemplary embodiment shownin FIG. 8 is calculated for an angle of approximately 45° from they-axis. The angle Θ is represented by arrows 804. The values from theelements along vectors in the angle Θ are multiplied by each other toyield a value calculated along each vector. The values calculated alongeach vector are represented by line graph 806. Line graph 806 reaches amaximum value at a point 807 corresponding to the position of theline-shaped echo pattern 322 on the 2D aperture 802. After values havebeen calculated for all of the vectors, all the values are addedtogether as represented by step 808. The MRT for the angle Θ representsthe sum of the values from all the vectors disposed at the given angle Θas expressed below in equations 1 and 2:

$\begin{matrix}{{{MRT}\left( {\theta,t} \right)} = {\frac{1}{M \star N}{\sum_{\rho}{\prod_{{- M}/2}^{\frac{M}{2} - 1}{\prod_{{- N}/2}^{\frac{N}{2} - 1}{v_{d} \cdot T}}}}}} & (1) \\{v_{d} = {{{v\left( {x,y,{t - \tau_{m,n}}} \right)}\mspace{14mu} {and}\mspace{14mu} T} = {\delta \left( {{x\; \cos \; \theta} + {y\; \sin \; \theta} - \rho} \right)}}} & (2)\end{matrix}$

where v is the instantaneous echo amplitude, τ_(m,n) is the delay, p isthe sampling location in the direction of MRT calculation as shown inthe figure, δ is the Dirac delta function to sample the grid in thedirection of MRT, N&M are the number channels of the array.

FIG. 9 is a representation showing an echo pattern and a correspondingMRT for three different orientations of a coherent reflector accordingto an exemplary embodiment. A first echo pattern 902 and a first graph904 are based on a coherent reflector disposed at an angle of 0° withrespect to an x-direction 310 in the x-y plane. A second echo pattern906 and a second graph 908 are based on a coherent reflector disposed atan angle of 40° with respect to the x-direction 310 in the x-y plane. Athird echo pattern 910 and a third graph 912 are based on a coherentreflector disposed at an angle of 80° degrees with respect to thex-direction 31 in the x-y plane. The data reflected in FIG. 9 wasacquired with a GE Vivid E95 using a 4V prove at 3 MHz on a Gammex403GS.

A y-axis 914 represents rows of the 2D aperture while a x-axis 916represents columns of the aperture. The first echo pattern 902 is agraphical representation of the amplitudes of a portion of the channeldata. The second echo pattern 906 and the third echo pattern 910 areboth also graphical representations showing rows of the aperture on ay-axis and columns of the aperture on an x-axis similar to the firstecho pattern 902. The first graph 904 represents MRT along a y-axis andangle along an x-axis 920. The second graph 908 and the third graph 912are both also representations showing MRT versus angle.

In the first graph 904, representing the MRT of ultrasound channel dataacquired with the coherent reflector at 0 degrees, the peaks 922 and 924of the MRT are shown at 0 degrees and at 180 degrees. In the secondgraph 908, representing the MRT of ultrasound channel data acquired withthe coherent reflector disposed at 40 degrees, the peak 926 of the MRTis shown at approximately 40 degrees. In the third graph 912,representing the MRT of ultrasound channel data acquired with thecoherent reflector at 80 degrees, a peak 928 of the MRT is shown atapproximately 80 degrees.

These three examples of coherent reflectors at 0 degrees, 40 degrees,and 80 degrees show how the MRT may be used to identify an angle of thecoherent reflector in the x-y plane. Calculating the MRT involvescalculating a coherence at a plurality of discrete angles from 0 degreesto 180 degrees. According to an exemplary embodiment, calculating theMRT may involve calculating the MRT at 1 degree increments from 0degrees to 180 degrees. However, it should be appreciated that otherembodiments may perform the MRT calculations at different intervals. Forexample, some embodiments may calculate MRT at increments that are lessthan 1 degree, while others may calculate the MRT at intervals greaterthan 1 degree. However, it is desirable to calculate the MRT at a enoughdiscrete angles so the controller 116 may determine an angle of maximumMRT.

Referring back to step 204 of the method 200 shown in FIG. 2, thecontroller 116 calculates the MRT from the ultrasound channel data. Thisincludes calculating a MRT for a plurality of different angles based onthe ultrasound channel data. As described above with respect to FIG. 8,the controller 116 may calculate the MRT for a plurality of differentangle using the ultrasound channel data. The controller 116, may forinstance calculate the MRT for every integral angle between 0 degreesand 180 degrees at 1 degree increments. According to other embodiments,the controller 116 may calculate the MRT at intervals that are eithergreater than 1 degree or less than 1 degree. According to preferredembodiments, the spacing between the adjacent angles, or samples, may beless than 10 degrees in order to obtain a resolution of less than 10degrees when determining the orientation of the coherent reflector.

At step 206, the controller 116 identifies a first angle α of aprojection of the coherent reflector onto a plane parallel to the 2Daperture, also referred to as the x-y plane. As previously discussedwith respect to FIG. 6, the controller 116 may, for instance, identifyan angle where the MRT is at a maximum in order to identify the firstangle α (shown in FIG. 8). The first angle α represents the angle in thex-y plane from the x-axis. A line 320 is shown in the 2D aperture 304that is used to illustrate the first angle α. The line 320 is aprojection of the coherent reflector 302 on the 2D aperture 304 (x-yplane). According to another embodiment, the controller 116, mayidentify either an angle or a range of angles that are above apredetermined threshold and then use either the angle or the range ofangles to calculate the first angle α.

At step 208, the controller 116 detects a line-shaped echo pattern 322based on the ultrasound channel data. The line-shaped echo pattern 322represents a reflection from the coherent reflector in a direction thatis perpendicular to the longitudinal axis 306 as shown in FIGS. 3, 4,and 7.

At step 210 the controller 116 determines a second angle β of thecoherent reflector 302 with respect to the 2D aperture 304. FIG. 5 showsthe coherent reflector 302 with respect to the 2D aperture 304.Controller 116 uses the position of the line-shaped echo pattern 322 todetermine the second angle β of the coherent reflector 302 with respectto the 2D aperture 304. The position of the line-shaped echo pattern 322will shift in a direction parallel to line 320 due to the angle of thecoherent reflector 302 with respect to the 2D aperture 304. Thecontroller 116 starts with a known position of the incident line 502from the transmit aperture 304 and a known focal position of theincident line 502. The controller 116 then detects the position of theline-shaped echo pattern and, based on the geometry of the transmitbeam, the focal position, the line-shaped echo pattern 322, and the apriori knowledge that the angle of incidence equals the angle ofreflection for a coherent reflector, the controller 116 calculates theangle of the coherent reflector that would result in the line-shapedecho pattern in the detected position. As shown in FIG. 5, the anglebetween the incident line 502 and the reflected beam 504 is 2*β. Thesecond angle β may be calculated based on the geometry shown in FIG. 5.

At step 211, the controller 116 uses the first angle α and the secondangle β to determine the position and orientation of the coherentreflector 302. The controller 116 uses the geometrical relationshipbetween the transmit beams, focal points, the first angle α and thesecond angle β to calculate the position and orientation of the coherentreflector 302.

At step 213, the controller 116 uses the position and orientationinformation of the coherent reflector 302 that was calculated at step211 to enhance a representation of the coherent reflector. Thecontroller 116 may enhance a representation of the coherent reflector inan image generated based on the ultrasound channel data. Enhancing therepresentation of the coherent reflector in the image may includegenerating a graphical indicator representing the coherent reflector anddisplaying the graphical indicator on the image. The graphical indicatormay include a line, an arrow, a cylinder, or any other graphical objectthat may be used to represent the position and orientation of thecoherent reflector. According to some embodiments, the graphicalindicator may include highlighting the portion of the image representingthe coherent reflector in a different color.

At step 216, the controller 116 displays the image, including theenhanced representation of the coherent reflector on the display device118.

According to other embodiments, enhancing the representation of thecoherent reflector may include modifying the beamforming using the MRT.A conventional delay-and-sum beamforming technique is shown below inequation 3:

$\begin{matrix}{{s(t)} = {\frac{1}{N}{\sum_{{n = 1},{m - 1}}^{N,M}{v\left( {t - \tau_{n,m}} \right)}}}} & (3)\end{matrix}$

where s is the sum, v is the instantaneous echo amplitude, τ_(n,m) isthe delay correction applied, N and M are the number of channels of thearray. FIG. 10 is a schematic representation of a conventionaldelay-and-sum beamforming technique. FIG. 10 includes a first column940, with elements number E₁, E₂, . . . , E_(N), where N represents thetotal number of elements. A second column 942 represents the delaysapplied to the ultrasound data from each of the elements. The delays arerepresented as T₁, T₂, . . . , T_(N). At 944, all of the signals aresummed together after the appropriate delays have been applied. Thestandard delay-and-sum approach therefore sums data from all of theelements acquired at a specific depth.

However, instead of using delay-and-sum beamforming, according to anembodiment, the controller 116 may use the values of the MRT at theangle where the MRT is at a maximum for each location. The MRT functionis shown below in equation 2:

d(t)=MRT(θ_(max) ,t)  (4)

where d is the MRT factor at θ_(max), and t is time. For example,according to an embodiment, the controller 116 may assign a value toeach pixel or voxel based on the value MRT(θ_(max)) for that particularpixel or voxel. Pixels or voxels that represent a coherent reflectorwill have a relatively high MRT at θ_(max). In contrast, pixels orvoxels that represent a diffuse reflector, such as soft tissue or fluid,will have a relatively low MRT at θ_(max). Using the MRT at θ_(max) todetermine pixel or voxel values when generating an image will result inan image that weights the coherent reflector more strongly than thenon-specular portions of the image.

FIG. 11 shows a schematic representation of using values from the MRT inplace of delay-and-sum beamforming in accordance with an exemplaryembodiment. FIG. 11 includes a first column 950 representing elementsE₁, E₂, . . . , E_(N). FIG. 11 includes a second column 952 representingthe delays applied to the data from each of the respective elements. Thedelays are represented as T₁, T₂, . . . , T_(N). After the delays havebeen applied to the data from the elements, the controller 116calculates the MRT at θ_(max) based on the data with the delays applied.For purposes of this disclosure, the technique schematically illustratedin FIG. 11 will be referred to as delay-and-MRT beamforming.

FIG. 12 shows a schematic representation of using values from the MRT inplace of delay-and-sum beamforming in accordance with an exemplaryembodiment. FIG. 12 includes a first column 960 representing elementsE₁, E₂, . . . , E_(N). FIG. 11 includes a second column 962 representingfilters that filter the data from each of the elements. FIG. 11 includesa third column 964 representing the delays applied to the data from eachof the respective elements. The delays are represented as T₁, T₂, . . ., T_(N). After the delays have been applied to the data from theelements, the controller 116 calculates the MRT at θ_(max) based on thefiltered data with the delays applied. For purposes of this disclosure,the technique schematically illustrated in FIG. 12 will be referred toas delay-filtered-and-MRT beamforming.

FIG. 13 is a table 970 showing a comparison between images generatedusing a conventional delay-and-sum beamforming and images generated froma delay-and-MRT beamforming according to an exemplary embodiment. Thetable 970 shows the results of different beamforming techniques appliedto the same data. For example, a first column 972 shows the results fromultrasound channel data acquired with the coherent reflector at 0degrees with respect to the x-axis on the 2D aperture. A second column974 shows the results from a ultrasound channel data acquired with thecoherent reflector at an angle of 40 degrees with respect to the x-axison the 2D aperture. And a third column 976 shows the results fromultrasound channel data acquire with the coherent reflector at an angleof 80 degrees with respect to the x-axis on the 2D aperture. The table970 includes a first b-mode image 978, a first MRT b-mode image 979, asecond B-mode image 980, a second MRT b-mode image 981, a third b-modeimage 982, and a third MRT b-mode image 983. The b-mode images, namelythe first b-mode image 978, the second b-mode image 980, and the thirdb-mode image 982 were each generated using a traditional delay-and-sumbeamforming approach. The MRT b-mode images, i.e., the first MRT b-modeimage 979, the second MRT b-mode image 981, and the third MRT b-modeimage 983 were each beamformed using the delay-and-MRT beamformingdescribed with respect to FIG. 11.

A line 984 represents the coherent reflector in the first b-mode image978, while a line 985 represents the coherent reflector in the first MRTb-mode image 979. A line 986 represents the coherent reflector in thesecond b-mode image 980, while a line 987 represents the coherentreflector in the second MRT b-mode image 981. A line 988 represents thecoherent reflector in the third b-mode image 982, while a line 989represents the coherent reflector in the third MRT b-mode image 983. Itis qualitatively apparent that the contrast ratio between the coherentreflectors and the rest of the image is much higher for the images thatwere beamformed using the delay-and-MRT technique compared to the imagesthat were beamformed using the conventional delay-and-sum beamformingtechnique.

The contrast ratio was calculated on the ultrasound channel data usingthe following equation:

$\begin{matrix}{{CR} = {20 \star {\log \; 10\left( \frac{I_{specular}}{I_{surrounding}} \right)}}} & (5)\end{matrix}$

where CR is the contrast ratio, I_(specular) is the intensity of theportion of the image representing the coherent reflector andI_(surrounding) is the intensity of the non-specular portions of theimage (i.e., all the portions of the image other than the coherentreflector). The contrast ratios of an image beamformed using thedelay-and-MRT beamforming technique discussed above was found to beapproximately 4 times the contrast ratios of an image beamformed usingthe conventional delay-and-sum technique on the same ultrasound channeldata. Table 1 shows the experimental results of the contrast ratiosobtained using three different beamforming techniques: conventionalb-mode (delay-and-sum), delay- and variance, and MRT b-mode (i.e.,delay-and-MRT beamforming). The contrast ratios were obtained on a VividE95.

TABLE 1 Orientation of needle/catheter (approximate ground truth)-α α =0° α = 40° α = 80° Conventional −23 dB −31 dB −26 dB B-mode Delay and−42 dB −58 dB −57 dB Variance MRT B-mode −96 dB −127 dB  −101 dB 

Referring back to FIG. 2, at 218, the controller 116 determines if thecoherent reflector 302 should be tracked. If the coherent reflector 302should not be tracked, then the method ends at 219. If the coherentreflector should be tracked, then the method 200 advances to step 220.At step 220, the controller controls the transmit beamformer 101, thetransmitter 102, the probe 106, the receiver 108 and the processor 110to acquire 2D ultrasound data including the coherent reflector 302. Thecontroller 116 may cause the transmit beamformer 101 to control theposition of the plane or frame from which the 2D ultrasound data isacquired to include the coherent reflector 302. For example, accordingto a first embodiment, the controller 116 may control the plane toinclude a straight portion of the coherent reflector 302. In otherwords, the plane of the 2D ultrasound acquisition may be positioned sothat the coherent reflector 302, or at least the straight portion of thecoherent reflector 302, is within the plane. According to otherembodiments, the controller 116 may steer the frames to acquire 3D dataincluding the coherent reflector.

FIG. 14 is a schematic representation of illustrating how the controller116 may beam steer in order to acquire ultrasound channel data includingthe coherent reflector 302. FIG. 14 includes the 2D aperture 304, thecoherent reflector 302, the longitudinal axis 306, the x-axis 310, they-axis 312, the first angle α, a first 2D frame 990, and a second 2Dframe 992. According to an embodiment, the ultrasound imaging system 100may initially acquire ultrasound data representing the first 2D frame990. However, after determining the position and orientation of thecoherent reflector 302 at step 211 of the method 200, the controller 116may use the position and orientation information to steer the 2D frameso it includes the coherent reflector 302 with the longitudinal axis 306lying inside the second 2D frame 992. For example, the second frame 992is an example of a 2D frame that has been steered to include thecoherent reflector 302. The second 2D frame 992 is oriented so that itpasses through the coherent reflector 302 along the longitudinal axis306. While steps 220 was described according to an embodiment where thedata was 2D data, according to other embodiments, the controller 116 mayacquire 3D data including the coherent reflector 302 based on theposition and orientation of the coherent reflector 302. According to anembodiment, the steps 202, 204, 206, 208, 210, 211, 213, 216, 218, 220,and 222 may be iteratively repeated multiple times as the coherentreflector 302 is moved. For example, if the coherent reflector is aninterventional device, like a biopsy needle, an operator may adjust theposition and orientation of the biopsy needle in order target thedesired structure in a patient's body. By iteratively repeating steps202, 204, 206, 208, 210, 211, 213, 216, 218, 220, and 222 the method 200adjusts the position of the 2D frame so that it tracks the position ofthe coherent reflector 302 as it moves. Acquiring 2D frames of thecoherent reflector 302 allows for high spatial and temporal resolution,which may aid the clinician in accurately positioning the coherentreflector 302. For embodiments where the data acquired at step 220 is 3Ddata, the volume-of-interest may be smaller than the volume-of-interestacquired at step 202 in order to provide improvements in spatial and/ortemporal resolution. This provides the clinician with a live imageshowing the position of the coherent reflector 302 with respect to thepatient's anatomy as the coherent reflector is repositioned in thepatient's body. The clinician may use this information to more accurateperform the desired interventional procedure. According to otherembodiments, the method 200 may be modified to omit some of the stepsthat were previously described. For example, some embodiments may notinclude steps 220 and 222. They may instead enhance the coherentreflector 302 at step 213 and display the image with the enhancedcoherent reflector. Other embodiments may omit steps 213 and 216. Theymay instead use the information about the position and orientation ofthe coherent reflector 302 to perform steps 220 and 222. Theseembodiments would provide the clinician with a real-time image showingthe position of the coherent reflector 302. Still other embodiments mayomit step 216. The controller 116 may use the position and orientationinformation determined at step 211 in order to control the acquisitionof the coherent reflector 302 at step 220. For example, the only imagesdisplayed to the user on the display device 118 may displayed at step222. The images displayed at step 22 may be a 2D image plane of theplane including the coherent reflector 302 or a 2D reformation of the 3Dvolume acquired to include the coherent reflector 302. The 2Dreformation of the 3D volume may be based on either the ultrasoundchannel data acquired at step 202 or on the smaller volume of dataacquired at step 220 according to various embodiments.

According to an embodiment where the method 200 iteratively repeat steps202, 204, 206, 208, 210, 211, 213, 216, 218, 220, and 222, thecontroller 116 may use the position and orientation information fromstep 211 to adjust the acquisition of ultrasound channel data at step202. For example, the controller 116 may use position and orientationinformation of the coherent reflector 302 determined at step 211 toacquire a smaller volume-of-interest or region or interest at step 220.This will still capture the coherent reflector 302 and it will enableimprovements in one or both of spatial resolution and temporalresolution.

Referring back to step 213, according to another embodiment, thecontroller 116 may generate a fused image to enhance the coherentreflector. For example, the fused image may be a fusion of a b-modeimage generated from a conventional dealy-and-sum beamforming technique,like that which was described with respect to FIG. 10 and a beamformingtechnique using the MRT. For example, the image generated withdelay-and-sum beamforming may be fused with an image generated fromeither delay-and-MRT beamforming (shown in FIG. 11) orfilter-delay-and-MRT beamforming (shown in FIG. 12). The fused imagewould advantageously show surrounding anatomical data from the imagegenerated from delay-and-sum beamforming and improve the contrast of thecoherent reflect based on the image generated from either thedelay-and-MRT beamforming or the filter-delay-and-MRT beamforming.

FIG. 15 is a schematic representation of a displayed image 999 includinga graphical indicator 1000 according to an exemplary embodiment. Thegraphical indicator 1000 serves as an enhanced representation of thecoherent reflector. The controller 116 may, for instance, display image999 at step 216. The graphical indicator 1000 comprises a line, but asdescribed above, the graphical indicator 1000 may comprise and icon oranother shape to convey the position and orientation of the coherentreflector according to other embodiments.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

We claim:
 1. A method for detecting a coherent reflector with anultrasound imaging system including a processor, the method comprising:acquiring ultrasound channel data from a volume with a probe including a2D aperture; calculating, with the processor, a MRT from the ultrasoundchannel data; identifying with the processor a first angle of aprojection of the coherent reflector in a plane parallel to the 2Daperture based on the MRT; detecting with the processor a line-shapedecho pattern in the ultrasound channel data; determining, with theprocessor, a second angle of the coherent reflector with respect to the2D aperture based on the position of the line-shaped echo pattern;determining, with the processor, a position and an orientation of thecoherent reflector based on the first angle and the second angle;enhancing a representation of the coherent reflector in an imagegenerated based on the ultrasound channel data; and displaying the imageon a display device after enhancing the representation of the coherentreflector.
 2. The method of claim 1, wherein enhancing therepresentation of the coherent reflector comprises generating agraphical indicator representing the coherent reflector and displayingthe graphical indicator on the image.
 3. The method of claim 2, wherethe graphical indicator comprises a line, an arrow, or a cylinder. 4.The method of claim 1, wherein enhancing the representation of thecoherent reflector comprises using the MRT to generate the image.
 5. Themethod of claim 4, wherein using the MRT to generate the image comprisesusing a delay-and-MRT beamforming.
 6. The method of claim 1, whereinenhancing the representation comprises generating a fused image, wherethe fused image comprises a b-mode image combined with an imagegenerated using a delay-and-MRT beamforming.
 7. The method of claim 1,further comprising acquiring additional ultrasound channel dataincluding the coherent reflector based on the position and theorientation of the coherent reflector.
 8. The method of claim 7, wherethe additional ultrasound channel data comprises 2D ultrasound data of aplane including the coherent reflector.
 9. The method of claim 7,wherein the additional ultrasound channel data comprises 3D ultrasounddata of a second volume including the coherent reflector, where thesecond volume is smaller than the volume.
 10. The method of claim 7,further comprising tracking the coherent reflector in real-time based onthe position and the orientation of the coherent reflector.
 11. Themethod of claim 8, further comprising adjusting a position of the planein real-time to track the coherent reflector based on the position andthe orientation of the coherent reflector.
 12. An ultrasound imagingsystem comprising: a probe including a 2D aperture; a display device;and a processor in electronic communication with the probe and thedisplay device, wherein the processor is configured to: control theprobe to acquire ultrasound channel data from a volume; calculate a MRTfrom the ultrasound channel data; identify a first angle of a projectionof the coherent reflector on a plane parallel to the 2D aperture basedon the MRT; detect a line-shaped echo pattern in the ultrasound channeldata; determine a second angle of the coherent reflector with respect tothe 2D aperture based on the position of the line-shaped echo pattern;determine a position and an orientation of the coherent reflector basedon the first angle and the second angle; enhance a representation of thecoherent reflector in an image generated based on the ultrasound channeldata; and display the image on the display device after enhancing therepresentation of the coherent reflector.
 13. The ultrasound imagingsystem of claim 12, wherein the processor is configured to enhance therepresentation of the coherent reflector by generating a graphicalindicator representing the coherent reflector and displaying thegraphical indicator on the image.
 14. The ultrasound imaging system ofclaim 12, wherein the processor is configured to enhance therepresentation of the coherent reflector by using the MRT to generatethe image.
 15. The ultrasound imaging system of claim 14, wherein theprocessor is configured to use a delay-and-MRT beamforming to generatethe image.
 16. The ultrasound imaging system of claim 12, wherein theprocessor is configured to enhance the representation of the coherentreflector by generated a fused image comprising a b-mode image combinedwith an image generated using a delay-and-MRT beamforming.
 17. Theultrasound imaging system of claim 12, wherein the processor isconfigured to acquire additional ultrasound channel data including thecoherent reflector based on the position and the orientation of thecoherent reflector.
 18. The ultrasound imaging system of claim 17,wherein the processor is further configured to track the position andthe orientation of the coherent reflector in real-time.
 19. Theultrasound imaging system of claim 18, where the additional ultrasoundchannel data comprises 2D ultrasound data of a plane including thecoherent reflector, and wherein the processor is further configured toadjust a position of the 2D plane in real-time to track the coherentreflector based on the position and the orientation of the coherentreflector.
 20. The ultrasound imaging system of claim 18, where theadditional ultrasound channel data comprises 3D ultrasound data of asecond volume that is smaller than the volume, where the second volumeincludes the coherent reflector, and wherein the processor is furtherconfigured to adjust a position of the second volume in real-time totrack the coherent reflector based on the position and orientation ofthe coherent reflector.